test: migrate tap suite to node:test

[mcollina]

Summary

• migrate remaining Tap-based tests to node:test
• replace Tap assertions in test/start.test.js via a local compat wrapper
• migrate test/graceful-shutdown.test.js to node:test
• remove Tap usage from examples/plugin-with-preloaded.js
• switch npm test scripts from Tap CLI to suite-runner.js
• remove tap and @types/tap from devDependencies

Validation

• node --test test/start.test.js
• node --test test/graceful-shutdown.test.js

[climba03003]

Using const { test: nodeTest } = require('node:test') and keep the test() in all files
More consistence usage and easier to migrate if we plan to use another test framework.

[mcollina]

Addressed review feedback:

• switched to const { test: nodeTest } = require('node:test') in test/graceful-shutdown.test.js
• kept test(...) usage consistently by defining const test = ... ? ... : nodeTest

Validation:

• node --test test/graceful-shutdown.test.js (pass)

[climba03003]

LGTM.